The present application relates generally to solar energy systems for the conversion of solar radiation to useful forms of energy, such as electrical and thermal energy as commonly generated by photovoltaic panels and solar-thermal panels.
Current photovoltaic panels (“solar panels” or “modules” are other terms commonly used), derive electrical current by the conversion of photon energy from the sun to electron energy by means of the photo-electric effect. However, current photovoltaic panel technology has limitations in the amount of energy that can be converted in the active layers of the panel. Different technologies are known that convert photon energy with higher or lower efficiency. Typically thin “wafer”-slices are of a material are cut from a block or crystal. Wafer shaped materials such as Gallium Arsenide (GaAs) have demonstrated conversion efficiencies as high as 40%. Other wafers commonly used are monocrystalline silicon (c-Si) and polycrystalline silicon (p-Si), with demonstrated conversion efficiencies of up to 20%. However, in practice, an efficiency between 12% and 18% is fairly common. Newer thin-film photovoltaic layers, which do not use wafer-like substrates, such as amorphous silicon (a-Si), micro-crystalline silicon (u-Si), and thin layers such as Cadmium Telluride (CdTe) and Copper Indium Gallium Selenide (CIGS) as well as polymer organic based active layers, are being pursued. Each of these technologies exhibits some level of energy conversion efficiency for some level of manufacturing cost. Oftentimes the economical considerations evolve around a cost per Watt of energy produced. The thin-film technologies above, typically demonstrate lower conversion efficiencies but do so at a lower manufacturing cost, which makes them viable for economically competitive photovoltaic applications. In other applications, the square footage of the photovoltaic installation is important because of space limitations. In those application c-Si or p-Si are preferred because even though they have a higher manufacturing cost, they use up less valuable space. Other concerns, such as the reliability of the film quality over the anticipated life of the product (which is oftentimes desired to be in the range of 30 years) as well as the concerns of dealing with some of the waste products of the manufacturing process (Arsenic, Cadmium, etc.) need to be taken into account when designing modules for photovoltaic applications. Furthermore, the environment in which the photovoltaic modules are used has a significant impact on the performance of the product. This involves elements such as orientation of the panel towards the sun, shading on the panel from nearby obstructions such as trees and other obstacles that can block a portion of a panel or entire panels and the weather, temperature, and wind in the location where the panel is expected to operate. For example, panels covered with snow can exhibit significantly reduced electrical production.
Additional considerations for cost effectiveness of photovoltaic products involve the cost of the system installation and the cost of the needed peripheral devices such as batteries or energy storage devices, DC to AC inverters, tracking systems (which have the ability to keep the panel oriented in the proper direction), and integrated system controllers.
Current photovoltaic panels capture only a small portion of the incident energy. Around 80% of the incident energy is not captured and either reflected back into the atmosphere or is re-emitted as radiation, which is typically in the infrared range. The manufacturing cost of the current solutions is relatively high for both wafer based panels and thin film based panels and the light conversion efficiency deteriorates over time due to the exposure of materials to the incident radiation and because of thermal effects in the active photovoltaic layers.
On the other hand, solar energy can also be captured by systems commonly known as solar hot water panels. In such panels, the solar radiation is captured on a surface that is thermally connected to a liquid reservoir or channel. The solar radiation is transferred as heat to the liquid, which is often water or a water-glycol mixture or some other thermal transfer fluid. The heated liquid is then transferred to a tank where it is stored and accumulated until it is needed. Oftentimes heat exchangers are used to withdraw the heat from the storage tank. Commonly such systems are implemented as either pressurized systems that are close-looped and where the liquid is always present in the solar hot water panels, or as drain-back systems, where the liquid is circulated and heated when there is adequate solar energy to increase the temperature of the heat transfer fluid and subsequently the liquid is removed when there is inadequate solar energy.
Solar electrical panels and solar hot water panels are commonly employed on buildings to capture as much incident radiation as possible and to convert such incident radiation to useful forms of energy, whether that is electrical or heat. Electrical panels are commonly connected in series or in parallel to other panels and ultimately connected to an electrical management and conversion system such as an inverter or power distribution panel. The goal of the balance of the system is to maximize the efficient production of electrical energy so that the building's reliance on the electrical grid can be reduced or even eliminated. Inverters are used to connect several chains of panels together and to control the production of AC electrical power. Such inverters oftentimes also control battery banks, manage critical loads, and can start emergency standby power generators.
Similarly, solar hot water panels are connected in series or in parallel, so that a maximum amount of hot liquid is produced at times when such production is most efficient. Again, a central controller is oftentimes employed to manage other system components such as pumps, thermocouples, and valves.